1、Public Lessons Learned Entry: 2536 Lesson Info: Lesson Number: 2536 Lesson Date: 2010-03-30 Submitting Organization: JPL Submitted by: David Oberhettinger Subject: Excess Cooling of MRO HiRISE Sunshade Abstract: A routine in-flight MRO spacecraft sequence placed the HiRISE instrument in an attitude
2、where the sunshade was shaded for an extended period. This unexpectedly caused the sunshade to drop below the allowable flight temperature, where thermal stress could damage the structure. Due to budget pressures, the instrument contractor had failed to update the integrated spacecraft thermal model
3、 to reflect changes to the thermal blanket design. Systems with a complex thermal design, like HiRISE, require an accurate and up-to-date thermal model. Description of Driving Event: Mars Reconnaissance Orbiter (MRO) was launched in August 2005 with a mission to study the Martian climate, identify w
4、ater-related landforms and aqueous deposits, characterize potential landing sites for Mars landers, and provide UHF relay for science data produced by these future missions. One of 6 science instruments on MRO, the High Resolution Imaging Science Experiment (HiRISE) camera, is designed to image the
5、Martian surface at up to five times the resolution previously available. Three months after launch, a spacecraft thruster calibration activity placed the spacecraft in an attitude that caused the temperature of the HiRISE sunshade (Figures 1 and 2) to unexpectedly drop to -136 degrees C (References
6、(1) and (2). This exceeded its lower temperature limit of -110 degrees C. established during qualification test. Because this attitude blocks data downlink to Earth, mission controllers did not detect this anomalous condition until the calibration activity was complete and the sunshade had returned
7、to its nominal temperature. The resulting thermal stress raised the concern of potential structural damage to the sunshade during this temperature excursion. . Figure 1. Diagram of HiRISE configuration Figure 2. Sunshade configuration is depicted in photo of HIRISE under construction Initial thermal
8、 analysis had predicted in-flight temperatures well within the allowable flight temperature (AFT), and the in-flight thermal performance to date had been consistent with the original thermal model. However, an investigation of the temperature excursion anomaly found that the validity of the spacecra
9、ft thermal model was compromised by two factors: 1. Although the sunshade is always exposed to the sun during nominal operations, it was shaded during the thruster calibration activity. One of the materials in the multi-layer insulation (MLI) thermal blanket had a coefficient of thermal expansion (C
10、TE) that was high enough for the shaded blanket to contract and contact the underlying sunshade, forming an unanticipated thermal short. 2. Design changes had been made to the thermal blanket, but due to budget pressures the HiRISE contractor did not update the integrated spacecraft thermal model to
11、 reflect the as-built thermal blanket. Because the behavior when shaded was unexpected, and because the sunshade is always exposed to the sun during nominal operations, updating the blanket model was not considered a high priority. Provided by IHSNot for ResaleNo reproduction or networking permitted
12、 without license from IHS-,-,-When the contractor subsequently updated the thermal model and ran it against the thruster calibration sequence, the results were in close agreement (within 1 degree C) with the flight actuals. A structural analysis indicated a positive stress margin for the sunshade du
13、ring the event; the absence of sunshade damage is also supported by instrument telemetry and image quality that show no signs of degradation in instrument performance or thermal properties. Future maneuvers have been modified as necessary to minimize sunshade shading. References: 1. “HiRISE Sunshade
14、 Temperature Exceeded Qualification Level During Thruster Cal,“ JPL Incident Surprise Anomaly (ISA) No. Z87738, November 3, 2005. 2. “HiRISE Sunshade temperature Exceeded Qualification Level During Thruster Cal,“ JPL Problem/Failure Report (PFR) No. Z87818, November 22, 2005. Lesson(s) Learned: The
15、in-flight thermal performance of systems with a complex thermal design, like HiRISE, is difficult to predict and requires an accurate and up-to-date thermal model. Had the thermal model been updated, the ramifications of the blanket design change would have been recognized. Recommendation(s): Prepar
16、e and use the most up-to-date integrated spacecraft thermal model whenever possible. Evidence of Recurrence Control Effectiveness: JPL has referenced this lesson learned as additional rationale and guidance supporting Paragraph 4.2.5.5 (“Mechanical Configuration/Systems Design: Structural Design - T
17、hermally-Induced Loading Factor Of Safety“) in the JPL standard “Design, Verification/Validation and Operations Principles for Flight Systems (Design Principles),“ JPL Document D-17868, Rev. 3, December 11, 2006. Documents Related to Lesson: N/A Mission Directorate(s): Space Operations Science Explo
18、ration Systems Aeronautics Research Additional Key Phrase(s): Additional Categories.Payloads Additional Categories.Hardware Additional Categories.Flight Operations Additional Categories.Flight Equipment Additional Categories.Environment Engineering Design (Phase C/D).Spacecraft and Spacecraft Instruments Additional Categories.Spacecraft Additional Info: Project: Mars Reconnaissance Orbiter Approval Info: Approval Date: 2010-05-19 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
